The complete genome of a novel mycovirus, Rhizoctonia solani dsRNA virus 1 (RsRV1) was sequenced and analyzed. It is composed of two dsRNA genome segments, 2379 bp and 1811 bp in length, which were referred to as RsRV1-1 and RsRV1-2, respectively. RsRV1-1 contains a single open reading frame (ORF1), which has a conserved RNA-dependent RNA polymerase (RdRp) domain, whereas RsRV1-2 contains a single ORF2, which might encode a multifunctional protein. The genome organization of RsRV1 is similar to that of members of the family Partitiviridae. However, phylogenetic analysis indicated that RsRV1 formed a distinct clade together with three other unclassified viruses, suggesting that RsRV1 may belong to a new family of dsRNA mycoviruses. This is the first report of the full-length nucleotide sequence of a novel dsRNA mycovirus, RsRV1, infecting R. solani AG-1 IA strain B275, the causal agent of rice sheath blight.